1. Field of the Invention
The present invention generally relates to a fuel evaporative emission control system for preventing evaporative emission of fuel gas which is produced within a fuel tank of an internal combustion engine. More particularly, the present invention relates to an abnormality detecting apparatus for detecting occurrence of abnormality such as leak of fuel gas in the fuel evaporative emission control system.
2. Description of the Related Art
In general, in the internal combustion engine for motor vehicles or the like, it is statutorily imposed to equip the engine with a fuel evaporative emission control system with the aim of preventing evaporative emission of the fuel gas produced within a fuel tank to the atmosphere.
The fuel evaporative emission control system of the type known heretofore is composed of a sensor unit for detecting operation states of the internal combustion engine (such as rotation speed and a load state of the engine), a purge passage for communicating the fuel tank provided for supplying the fuel to the engine and an intake pipe thereof with each other, and a canister disposed in the purge passage at an intermediate location thereof.
The canister adopted for adsorbing the fuel gas produced within the fuel tank has an atmospheric air port which can be opened to the atmosphere, and a purge control valve is disposed at an intermediate location between the canister and the intake pipe of the engine. An adsorbent disposed within the canister adsorbs the fuel gas on the way of flowing through the purge passage which communicates the fuel tank and the intake pipe with each other.
Further, the fuel evaporative emission control system includes a fuel evaporative emission control unit (constituted by a microcomputer) for controlling opening/closing operation of the purge control valve in dependence on the operation states of the internal combustion engine in order to sustain the fuel gas adsorbing function of the canister by preventing the adsorbent from becoming saturated.
The fuel evaporative emission control unit is so designed as to control opening/closing of the purge control valve in dependence on the operation states of the internal combustion engine for causing the fuel gas adsorbed by the canister to be discharged into the intake pipe such that the fuel gas is mixed with the mixture of air and fuel. In this manner, the evaporative emission of the fuel can be prevented.
Typically, the above-mentioned fuel evaporative emission control system is provided with an abnormality detecting apparatus for detecting closure of an atmospheric air port of a canister, inability to open a purge control valve, damage to a purge passage on a side of an air intake pipe, and other such abnormalities in the fuel evaporative emission control system, based on a fuel tank pressure (see, for example, JP 2002-357163 A).
In accordance with this abnormality detecting apparatus for detecting the abnormality in the fuel evaporative emission control system, the detection of leak abnormality in the fuel evaporative emission control system is prohibited, depending on a concentration of fuel gas which is generated at the fuel tank, adsorbed by the canister, and made to flow into the air intake pipe due to opening control of the purge valve. Thus, the abnormality detection precision is increased.
However, the fuel gas concentration is detected based on a purge air amount introduced into the air intake pipe from the canister by the opening control of the purge valve before performing the abnormality decision, and an operation state including an air-fuel ratio feedback signal. Therefore, the purge valve is closed to put the tank in a hermetically sealed state, and thus the influence on the fuel tank pressure due to a change in the fuel gas concentration in the abnormality decision processing is not considered. This causes a fear of deterioration of the abnormality detection performance and an erroneous detection.
Further, even with the same fuel temperature, the tendency of occurrence of the fuel evaporative emission inside the fuel tank varies depending on influence from an atmospheric pressure, even under the same fuel temperature, tank interior temperature, and external atmospheric temperature. Therefore, there is a fear of deterioration of the abnormality detection performance and the erroneous detection.
As described above, in the conventional abnormality detecting apparatus for a fuel evaporative emission control system, the purge valve is closed and the tank is set in the hermetically sealed state, and the influence of the fuel tank pressure during the processing of performing the abnormality decision is not considered. Therefore, due to differences in each environmental condition and the like, there is an adverse effect on the abnormality detection. Ultimately, there is a problem in that the abnormality detection cannot be made accurately.
The present invention has been made to solve the above-mentioned problems, and therefore has as an object to provide an abnormality detecting apparatus for a fuel evaporative emission control system, in which reliability is improved by setting a prohibition condition decision value for at least one of a fuel temperature, a tank internal temperature, and an external atmospheric temperature.
According to the present invention, an abnormality detecting apparatus for detecting abnormality in a fuel evaporative emission control system includes: a sensor unit for detecting operation states of an internal combustion engine; a canister disposed at an intermediate location of a purge passage communicating a fuel tank providing fuel to the internal combustion engine and an air intake pipe of the internal combustion engine with each other, for adsorbing fuel gas generated in the fuel tank; an atmospheric air port provided to the canister and opened to an atmosphere side; a purge valve disposed at an intermediate position between the canister and the air intake pipe; and a fuel evaporative emission control unit for preventing the evaporative emission of the fuel by controlling opening/closing of the purge valve depending on the operation state of the internal combustion engine and introducing fuel gas adsorbed by the canister into the air intake pipe as occasion requires.
Further, the sensor unit includes: one of an intake air amount detecting unit for detecting an intake air amount as a load state of the internal combustion engine, and an intake air pipe pressure detecting unit for detecting an intake air pressure and an atmospheric pressure detecting unit for detecting an atmospheric pressure; at least one of an outside air temperature detecting unit for detecting an outside air temperature, a fuel temperature detecting unit for detecting a fuel temperature inside the fuel tank, and a tank internal temperature detecting unit for detecting a gas temperature inside the fuel tank; and a fuel tank pressure detecting unit for detecting a pressure within the fuel tank as a fuel tank pressure.
Further, the fuel evaporative emission controlling unit includes: an atmospheric air port closing unit for closing the atmospheric air port; a hermetically closing unit for hermetically closing both the purge control valve and the and the atmospheric air port to thereby put the overall fuel evaporative emission control system in a hermetically sealed state; an abnormality decision enabling condition detecting unit for detecting validity of an abnormality decision enabling condition of the fuel evaporative emission control system, based on the operation state of the internal combustion engine; a purge rate adjusting unit for regulating a purge rate by controlling an opening degree of the purge control valve depending on the air intake pipe pressure when the abnormality decision enabling condition is valid; and an abnormality detecting unit for detecting an abnormality of the fuel evaporative emission control system, based on the fuel tank pressure at the time when the abnormality decision enabling condition is valid.
Further, the abnormality decision enabling condition detecting unit includes a condition validation limiting unit for prohibiting the abnormality decision, in dependence on at least one of the fuel temperature, the tank internal temperature, and the outside air temperature.